I'd like to speak up for the "negative" person (call her NP).
There is nothing in any of the previous posts that indicates any interest in NP's views. Not a single positive or negative idea is attributed to her.
Some PTSAs want to change the world but not themselves. Perhaps NP is focused on improving the PTSA before improving the school. Why not invite her to Starbucks (you pay), bring a notebook, and listen and write while she speaks? Some of her ideas might be doable and even useful. For example, does your PTSA, like many others, completely ignore the IRS' deadlines for filing a Form 990? Do you use Robert's Rules, or at least a diluted version? Do you have an agenda and monthly financial statements before meetings, and minutes afterward? Is the Wishlist of expenditures formed democratically, or arbitrarily by the person you want to be (President)?
I'm just trying to say that if there is smoke (NP's negative comments), there may be fire (real governance issues that should be addressed). Again, invite NP to coffee. She may have good ideas, or good skills (webmaster, accountant, lawyer, CRM, campaign manager, event manager, grant writer, etc). Just take an hour, back off, and listen. If it turns out she has a particular skill, invite her to use that skill in the following year.